5.3L Bow Tie Builds Mild To Wild

Power Recipes for the 5.3L LM7

They say variety is the spice of life, and that certainly holds true for Chevy truck owners. As difficult as it is to believe, the vast majority of trucks purchased remain bone stock. Modifications to these stockers tend to be more of the tree-shaped, air freshener variety than some performance enhancement underhood. Many owners don't even know where to find the hood latch, let alone what to modify once they successfully locate the engine bay. Truckin readers tend to populate the other end of the performance spectrum, a position unencumbered by pine-scented floral fixtures. Despite sharing a desire for performance, variety is still the order of the day. For some, it's a simple cam swap combined with an air intake and cat-back exhaust, while others go whole hog and opt for a maximum-effort, all-motor stroker. Recognizing (and applauding) this diversity, we decided to offer up a little variety of our own—Truckin style. When all was said and done, we tested no less than five different 5.3L combinations, including the stock motor, ranging from mild to wild. Check them out and decide which one is right for your Chevy truck.

Before running any of the modified combinations on the engine dyno, we needed power numbers on a stock motor. The 160.000-mile 5.3-liter was installed on the engine dyno and run with a FAST XFI/XIM management system. The LM7 was run with a set of QTP headers, a manual Accufab throttle body (our wrecking yard motor was not supplied with a stock throttle body) and a Meziere electric water pump. In otherwise stock trim, the 5.3-liter produced 356 hp at 5,400 rpm and 378 lb-ft of torque at 4,300 rpm. Tuned for towing, torque production exceeded 360 lb-ft from 3,700 rpm to 5,100 rpm. Even down at 2,500 rpm, the little 5.3-liter pumped out 345 lb-ft. Is it any wonder the affordable and powerful 5.3-liter is fast becoming the swap engine of choice?

For those looking to enhance the power output of their 5.3-liter without sacrificing throttle response and low-speed torque, this 5.3-liter is ideal. Using the stock short-block, we upgraded the heads and cam to dramatically improve the midrange and top end power without the usual trade off in low-speed torque. In fact, this combination improved the power output of the 5.3-liter from 2,500 rpm right through 6,500 rpm. The TrackMax cam from Trick Flow Specialties offered an excellent combination of power and idle quality. The combination of the ported 5.3L heads from Total Engine Airflow and mild TrackMax cam increased the power output of the 5.3-liter from 356 hp and 378 lb-ft of torque to 436 hp and 410 lb-ft of torque. You will want to reprogram the full-throttle shift points in your tranny to take advantage of the extra power at the top of the rev range.

This wild combination was designed to cater to the needs of the adventurous few who are looking to maximize the power output of their 5.3-liter. The stock 5.3L short-block was retained, but with one small change. The stock dished pistons were replaced with flat-top versions from the 4.8-liter. It is also possible to utilize an L33 HO version of the 5.3L factory equipped with flat-top pistons. The flat-tops were combined with a set of TFS GenX 205 heads designed specifically for the small-bore 4.8L/5.3L motors. The GenX heads offered tremendous flow while retaining the small combustion chamber to optimize the static compression ratio. The heads worked in conjunction with a COMP XR281HR cam and FAST LSXR intake. Run with lightweight Lucas synthetic oil, we managed to fine-tune this 5.3-liter up to 501 hp and 452 lb-ft of torque. Make no mistake, this motor was happiest higher in the rev range, but we were surprised by the torque production. Though we expected the combination of added head flow, cam timing, and runner volume in the LSXR intake to at least trade off low-speed torque, this combination offered more power and torque from 3,000 rpm to 7,000 rpm.

Though the 5.3L LM7 offers plenty of power in modified form, the torque production is ultimately limited by the displacement. The cure for this limitation is as simple as adding inches, in this case jumping from 324 ci to a full 383 ci. The increased displacement will improve not only peak power, but more importantly, average torque production. Basically the bigger motor can make more power everywhere. The additional displacement allows you to equal the power output of the wild 5.3-liter with a much milder combination. The benefit of going the stroker route is improved fuel mileage (over the wild-cammed 5.3-liter) and monster torque curve. The 5.3L block was bored to accept 3.902 forged pistons from Probe Racing, and then combined with a 4.0-inch stroker crank and 6.2-inch rods from Procomp Electronics. The stroker short-block was topped with the same TEA-ported 5.3L heads used on the mild 5.3-liter. Wanting a daily driver, we chose a mild COMP XR275HR cam. The combination offered plenty of power, peaking at 506 hp at 5,700 rpm and 503 lb-ft of torque at 4,700 rpm. Torque production was up by 100 lb-ft over the stock 5.3-liter at 3,000 rpm and by 90 lb-ft at 3,500 rpm.

Like the wild 5.3-liter, this 383 version pushed the limits of driveability, but boy howdy did it make power. Using a 5.3L block, we bored and stroked the 5.3-liter to achieve a final displacement of 383 ci. Unlike the mild version that featured a static compression of 9.5:1, this 383 was sporting flat-top pistons that pushed the static compression ratio to 11.0:1. The elevated compression ratio was combined with a set of TEA Stage 2.5 LS6 heads, an aggressive COMP 289LR HR14 cam and FAST LSRXT (truck) intake. Wanting to maximize power, we even installed a set of 1.72:1-ratio aluminum roller rockers and swapped out the 1¾-inch headers for larger 1⅞-inch versions from American Racing Headers. The extra breathing paid off, as the 5.3L 383ci stroker produced 603 hp and 544 lb-ft of torque. Torque production exceeded 525 lb-ft from 4,400 rpm to 5,900 rpm, making for one sweet torque curve.